trap: Implement signal handlers and the EXIT hook.

- Fix removal of hooks/signal handlers.
- Warn if the ERR, DEBUG, or RETURN hook is used.

Addresses issue #60.

bin/oil.py

@@ -406,7 +406,7 @@ def OshMain(argv, login_shell):

    if do_exec:
      _tlog('Execute(node)')
      status = ex.Execute(node)
      status = ex.Execute(node, run_exit_trap=True)

      # We only do this in the "happy" case for now.  ex.Execute() can raise
      # exceptions.

core/builtin.py

@@ -983,6 +983,30 @@ def DeclareTypeset(argv, mem, funcs):
import signal


class _TrapThunk(object):
  """A function that is called by Python's signal module.

  Similar to process.SubProgramThunk."""

  def __init__(self, ex, node):
    self.ex = ex
    self.node = node

  def __call__(self, unused_signalnum, unused_frame):
    """For Python's signal module."""
    self.Run()

  def Run(self):
    """For hooks."""
    unused_status = self.ex.Execute(self.node)

  def __str__(self):
    # Used by trap -p

    # TODO: Abbreviate with fmt.PrettyPrint?
    return str(self.node)


def _MakeSignals():
  """Piggy-back on CPython to get a list of portable signals.

@@ -1006,10 +1030,17 @@ def _MakeSignals():
TRAP_SPEC.ShortFlag('-p')
TRAP_SPEC.ShortFlag('-l')

# TODO:
#
# bash's default -p looks like this:
# trap -- '' SIGTSTP
# trap -- '' SIGTTIN
# trap -- '' SIGTTOU
#
# CPython registers different default handlers.  Wait until C++ rewrite to 

def Trap(argv, traps, ex):
  arg, i = TRAP_SPEC.Parse(argv)
  status = 0

  if arg.p:  # Print registered handlers
    for name, value in traps.iteritems():
@@ -1041,30 +1072,50 @@ def Trap(argv, traps, ex):

  # NOTE: sig_spec isn't validated when removing handlers.
  if code_str == '-':
    try:
      del traps[sig_spec]
    except KeyError:
      pass
    return 0
    if sig_spec in _HOOK_NAMES:
      try:
        del traps[sig_spec]
      except KeyError:
        pass
      return 0

    sig_val = _SIGNAL_NAMES.get(sig_spec)
    if sig_val is not None:
      try:
        del traps[sig_spec]
      except KeyError:
        pass

      # Restore default
      signal.signal(sig_val, signal.SIG_DFL)
      return 0

  # Try parsing code first.
    util.error("Can't remove invalid trap %r" % sig_spec)
    return 1

  # Try parsing the code first.
  node = ex.ParseTrapCode(code_str)
  if node is None:
    return 1  # ParseTrapCode() prints an error for us.

  # Register a hook
  # Register a hook.
  if sig_spec in _HOOK_NAMES:
    traps[sig_spec] = node
    if sig_spec in ('ERR', 'RETURN', 'DEBUG'):
      util.warn("*** The %r isn't yet implemented in OSH ***", sig_spec)
    traps[sig_spec] = _TrapThunk(ex, node)
    return 0

  # Register a signal
  # Register a signal.
  sig_val = _SIGNAL_NAMES.get(sig_spec)
  if sig_val is not None:
    traps[sig_spec] = node
    # TODO: call signal.signal()
    handler = _TrapThunk(ex, node)
    # For signal handlers, the traps dictionary is used only for debugging.
    traps[sig_spec] = handler

    signal.signal(sig_val, handler)
    return 0

  util.error('Invalid signal %r' % sig_spec)
  util.error('Invalid trap %r' % sig_spec)
  return 1

  # Example:

core/cmd_exec.py

@@ -133,7 +133,7 @@ def __init__(self, mem, fd_state, status_lines, funcs, completion,
    self.arith_ev = expr_eval.ArithEvaluator(mem, exec_opts, self.word_ev)
    self.bool_ev = expr_eval.BoolEvaluator(mem, exec_opts, self.word_ev)

    self.traps = {}  # signal/hook -> LST node
    self.traps = {}  # signal/hook name -> callable
    self.dir_stack = state.DirStack()

    # TODO: Pass these in from main()
@@ -1100,7 +1100,8 @@ def _Dispatch(self, node, fork_external):
    return status, check_errexit

  def _Execute(self, node, fork_external=True):
    """
    """Does redirects, calls _Dispatch(), and does errexit check.

    Args:
      node: of type AstNode
      fork_external: if we get a SimpleCommand that is an external command,
@@ -1160,9 +1161,28 @@ def _ExecuteList(self, children):
      status = self._Execute(child)  # last status wins
    return status

  def Execute(self, node, fork_external=True):
    """Execute a top level LST node."""
    # Use exceptions internally, but exit codes externally.
  def Execute(self, node, fork_external=True, run_exit_trap=False):
    """Execute a subprogram, handling _ControlFlow and fatal exceptions.

    Callers:
    - SubProgramThunk for pipelines, subshell, command sub, process sub
    - .oilrc
    - _TrapThunk
    - Interactive loop
    - main program

    Most other clients call _Execute():
    - _Source() for source builtin
    - _Eval() for eval builtin
    - RunFunc() for function call

    Args:
      node: LST subtree
      fork_external: whether external commands require forking

    Returns:
      status: numeric exit code
    """
    try:
      status = self._Execute(node, fork_external=fork_external)
    except _ControlFlow as e:
@@ -1176,7 +1196,14 @@ def Execute(self, node, fork_external=True):
      print('osh failed: %s' % e.UserErrorString(), file=sys.stderr)
      status = e.exit_status if e.exit_status is not None else 1
      # TODO: dump self.mem if requested.  Maybe speify with OIL_DUMP_PREFIX.
    finally:
      if run_exit_trap:
        # NOTE: The trap itself can call exit!
        thunk = self.traps.get('EXIT')
        if thunk:
          thunk.Run()

    # Other exceptions: SystemExit for sys.exit()
    return status

  def RunCommandSub(self, node):

spec/builtin-trap.test.sh

@@ -6,14 +6,19 @@ trap -l | grep SIGINT >/dev/null
## N-I dash/mksh status: 1

### trap -p
trap -p | grep trap >/dev/null
trap 'echo exit' EXIT
trap -p | grep EXIT >/dev/null
## status: 0
## N-I dash/mksh status: 1

### Register invalid trap
trap 'foo' SIGINVALID
## status: 1

### Remove invalid trap
trap - SIGINVALID
## status: 1

### Invalid trap invocation
trap 'foo'
echo status=$?

test/spec.sh

@@ -290,7 +290,7 @@ builtin-test() {
}

builtin-trap() {
  sh-spec spec/builtin-trap.test.sh --osh-failures-allowed 5 \
  sh-spec spec/builtin-trap.test.sh --osh-failures-allowed 3 \
    ${REF_SHELLS[@]} $OSH "$@"
}